Superconductor comprising a niobium substrate having a coating of niobium stannide and particles of a ferromagnetic material



P 1967 A. E. VAN ARKEL 8 SUPERCONDUCTOR COMPRISING A NIOBIUM SUBSTRATE HAVING A COATING OF NIOBIUM STANNIDE AND PARTICLES OF A FERRQMAGNETIC MATERIAL Filed Sept. 30, 1963 FERRITE PARTICLES United States Patent 3,341,308 SUPERCONDUCTOR CQMPRISING SUBSTRATE HAVING A COATING STANNIDE AND PARTICLES OF A NETIC MATERIAL Anton E. van Arkel, Leiden, Netherlands, assignor to National Research Corporation, Cambridge, Mass., a corporation of Massachusetts Filed Sept. 30, 1963, Ser. No. 312,737 4 Claims. '(Cl. 29-195) The present invention relates to superconductors and particularly to elongated superconductors in wire or ribbon form which can be wound into solenoids, armatures and other inductive coils.

It is the object of the invention to provide a way of distributing magnetic field more uniformly among the windings of a magnetic coil.

It is a further object of the invention to provide an insulator in contact with superconductive windings.

It is another object of the invention to provide a single material for use with superconductors which combines the qualities of ferromagnetism and high resistance at cryogenic temperatures.

In accordance with a preferred embodiment of the invention, a niobium ribbon coated with a superconducting layer of niobium stannide is further coated with a slurry of barium ferrite particles in water or a lacquer. The barium ferrite is a ceramic having the approximate composition BaFe O and also known as Magnadure. The resultant product has the particles of barium ferrite well distributed over its surface. When the product is cooled to liquid helium temperatures for superconductive operation, the barium ferrite particles will be ferromagnetic. Yet the high resistivity of the barium ferrite will limit the flow of eddy currents therein.

The resultant product, shown in the drawing, comprises a niobium layer, niobium stannide layers and an outer coating of organic material supporting ferrite particles.

While barium ferrite has been described as a preferred embodiment, it should be understood that other insulating materials may be used. Other ferrites are good insulators at cryogenic temperatures. Their 273 K. resis- A NIOBIUM OF NIOBIUM FERROMAG- tivities are above 10 to 10 ohm-cm, as compared with 10 ohm-cm. for iron. Cryogenic temperatures increase the resistivity of the ferrites. In simplest form, the ferrite group comprises compositions represented by the formula MeOFe O where Me is a divalent metal ion such as Ba, Mn, Co, Ni, Cu, Mg, Zn, Cd, Fe or a mixture of these ions. A second requirement is that the insulating material must be ferromagnetic at liquid helium temperature. Most of the ferrites have Curie points well above cryogenic temperatures. Cryogenic temperatures generally increase their saturation magnetization values.

Many materials, other than the ferrites, have high resistivities and high permeabilities and magnetic saturation values at cryogenic temperatures. For instance, particles of gadolimum oxide could be substituted for the ferrite particles described above.

What is claimed is:

1. A superconductive electromagnetic coil comprising therein distributed layers of ferromagnetic material for shunting magnetic fields in the coil at cryogenic temperatures, the material having a resistivity in excess of about 10 ohm-cm. at cryogenic temperatures.

2. The coil of claim 1 wherein the material has a composition selected from those ferrites whose magnetic saturation and resistivity increase with lowering of their temperatures into the cryogenic range.

3. The coil of claim 2 wherein the material is barium ferrite.

4. A niobium ribbon having a diffusion coating of niobium stannide and particles of barium ferrite distributed across the surface of the coated ribbon.

References Cited UNITED STATES PATENTS 2,970,961 2/1961 Matthias 117-235' X 3,110,613 11/1963 Bean 117-13O X 3,125,688 3/1964 Rogers 33 832 3,181,936 5/1965 Denny et a1. 29194 3,243,871 5/1966 Saur 29-1555 ALFRED L. LEAVITT, Primary Examiner. WILLIAM L. JARVIS, Examiner. 

1. A SUPERCONDUCTIVE ELECTROMAGNETIC COIL COMPRISING THEREIN DISTRUBUTED LAYERS OF FERROMAGNETIC MATERIAL FOR SHUNTING MAGNETIC FIELDS IN THE COIL AT CRYOGENIC TEMPERATURES, THE MATERIAL HAVING A RESISTIVITY IN EXCESS OF ABOUT 10**4 OHM-CM. AT CRYOGENIC TEMPERATURE. 